I'll soon be having both my washing machine and soon to purchase dryer under a bench top, but with my current front loader washer (and previous top loader washing machine), I just used to put a white towel/hand towel over the top.You could maybe try some of that non-stick matting??

We bought a rubber mat from The Good Guys since our dryer rests on the washer. Keeps them from scratching and shifting. On top of the dryer we have a small cotton mat from IKEA or something. It keeps the dryer clean from all the stuff on top (baskets, laundry soap, etc).